Everything You Need to Know about Narcissists, Psychopaths, and Abuse - click on this link: http://www.narcissistic-abuse.com/faq1.html
The narcissist regards his disabled or challenged child as an insult, a direct challenge to his self-perceived perfection and omnipotence, a constant, nagging source of negative narcissistic supply, and the reification and embodiment of a malevolent and hostile world which tirelessly conspires to render him a victim through misfortune and catastrophe. The precarious foundations of his False Self – and, therefore, his ability to function - are undermined by this miscegenation.
Relentlessly challenged by his defective offspring’s very existence and by the persistence of its attendant painful reminders, the narcissist lashes out, seeking to persecute and penalize the sources of his excruciating frustration: the child and his mother. The narcissist holds her responsible for this failure, not himself. She brought this shame and perturbation into his otherwise fantastic life. It was she who gave issue to this new fount of torment, this permanent reminder of fallibility, imperfection, mortality, impotence, guilt, disgrace, and fear.
To rectify this wrong, to restore the interrupted balance, and to firmly regain an assured sense of his grandiosity, the narcissist resort to devaluation. He humiliates, belittles, and demeans both the unfortunate child and his suffering mother. He compares their failings unfavourably to his own wholeness. He berates and mocks them for their combined disability, frailty, weakness, meekness, and resourcelessness. He transforms then into the captive butts of his unbridled sadism and the cowed adherents of a cult-like shared psychosis. Serves them well for having thus ruined his life, figures the narcissist.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 3 DVDs with 16 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)